research papers

446 doi:10.1107/S1600577515000314 J. Synchrotron Rad. (2015). 22, 446–451

Journal of

SynchrotronRadiation

ISSN 1600-5775

Received 13 May 2014

Accepted 7 January 2015

Ancient administrative handwritten documents:X-ray analysis and imaging

F. Albertin,a* A. Astolfo,b M. Stampanoni,b,c Eva Peccenini,d,e Y. Hwu,f F. Kaplang

and G. Margaritondoa

aFaculte des Sciences de Base, Ecole Polytechnique Federale de Lausanne (EPFL), CH-1015

Lausanne, Switzerland, bSwiss Light Source, Paul Scherrer Institut (PSI), Villigen, Switzerland,cInstitute for Biomedical Engineering, ETHZ, Zurich, Switzerland, dDepartment of Physics and Earth

Sciences, University of Ferrara, Italy, eLaboratory TekneHub, Technopole of Ferrara, Italy, fInstitute

of Physics, Academia Sinica, Taipei, Taiwan, and gLaboratoire d’Humanites Digitales, Ecole

Polytechnique Federale de Lausanne (EPFL), Switzerland. *E-mail: fauzia.albertin@epfl.ch

Handwritten characters in administrative antique documents from three

centuries have been detected using different synchrotron X-ray imaging

techniques. Heavy elements in ancient inks, present even for everyday

administrative manuscripts as shown by X-ray fluorescence spectra, produce

attenuation contrast. In most cases the image quality is good enough for

tomography reconstruction in view of future applications to virtual page-by-

page ‘reading’. When attenuation is too low, differential phase contrast imaging

can reveal the characters from refractive index effects. The results are

potentially important for new information harvesting strategies, for example

from the huge Archivio di Stato collection, objective of the Venice Time

Machine project.

Keywords: cultural heritage; ancient manuscripts; ancient inks; X-ray fluorescence;phase contrast; refractive index imaging; differential phase contrast.

1. Reading ancient handwritings: role of X-rays

We have correlated the chemical analysis by X-ray fluores-

cence spectroscopy (XRF, with a portable instrument) of 15th

to 17th century administrative Italian documents and the

X-ray imaging of the handwritten characters using synchro-

tron radiation. This combined approach has enabled us to

extensively and flexibly characterize the ink composition prior

to the imaging tests, then to exploit the properties of

synchrotron radiation for advanced X-ray imaging (including

refraction-based contrast when attenuation is weak) and

tomography, and finally to correlate the results.

Heavy elements in inks (Del Carmine et al., 1996) normally

allow their detection by X-ray attenuation. However, strong

concentration fluctuations occur between different manu-

scripts and between different areas of the same specimen.

Sometimes low concentration impedes detection by attenua-

tion; an alternative method is refractive-index contrast (Hwu

et al., 1999) in differential phase contrast imaging (Weitkamp

et al., 2005).

Our study is part of the international Venice Time Machine

(VTM) project (http://dhvenice.eu). The Archivio di Stato in

Venice holds about 80 km of archival documents spanning

over ten centuries and documenting every aspect of the

Venetian Mediterranean Empire. If unlocked and trans-

formed into a digital data system, this information could

change significantly our understanding of European history.

But the sheer mass of data is a problem. VTM plans to

digitalize and decipher the entire collection in 10–20 years.

To facilitate and accelerate this task, the project also

explores new ways to virtually ‘read’ manuscripts, rapidly and

non-invasively. We specifically plan to use X-ray tomography

to computer-extract page-by-page information from sets of

projection images. The raw data can be obtained without

opening or manipulating the manuscripts, reducing the risk of

damage and speeding up the process.

This approach is based on precursor projects exploiting

X-rays to decipher documents. Notably, synchrotron light was

used to retrieve ‘lost’ text from the ‘Archimedes Palimpsest’

(Bergmann, 2000) with X-ray fluorescence. The use of X-ray

tomography to analyze handwriting was pioneered by Seales

et al. (Lin & Seales, 2005; Baumann et al., 2008; Seales et al.,

2011) with the EDUCE project. A top-level program in this

direction was launched by T. Wess of Cardiff University (Mills

et al., 2012; Patten et al., 2013). In particular, the project

virtually ‘unrolled’ scrolls producing flat readable images and

assessed the possibility of damage by X-ray exposure.

These efforts are part of several pioneering studies

exploiting synchrotron techniques for the humanities and art

(Janssens, 2011; Creagh & Bradley, 2007; Caforio et al., 2014;

Morigi et al., 2010; Reischig et al., 2009; Dik et al., 2008, 2010;

Mozir et al., 2012; Faubel et al., 2007; Lucarelli & Mando, 1996;

Kennedy et al., 2004; Gunneweg et al., 2010; Murphy et al.,

2010). In general, such efforts have demonstrated high effec-

tiveness in clarifying issues, notably those related to chemical

and microstructural properties and their relations to issues

such as environment-related damage, origin, dating etc.

However, they still realise only a small fraction of the

potential applications of synchrotron experiments in these

domains.

Along the path to deciphering the Venice collection, we

must deal with a series of key issues. A fundamental one is the

nature of the ink in everyday documents (as opposed to pieces

of high artistic or historical value) and its detection by X-rays.

This is the subject of our present study.

The issue is by no means clear a priori. The very nature of

the VTM project requires studying archival documents such as

ship records, notary papers, work contracts, tax declarations,

commercial transactions and demographic accounts. For such

items, the ink composition is scarcely documented. Further-

more, the Archivio di Stato collection spans ten centuries, with

inevitable fluctuations in the ink chemistry.

Clarifying these issues has a remarkable and multi-faceted

potential impact. First, in addition to the Venice collection the

techniques could be applied to many documents at risk

throughout the world. Second, the chemical and micro-

structural information is also relevant for the deterioration

mechanisms and could help in preventing them.

Our main results are the following. First, heavy elements are

systematically detected in the inks of personal and commercial

documents over the three centuries investigated here. Second,

the chemical composition is basically consistent with the

historical records of the inks (Yale University Library Special

Collections Conservator Unit, 2012; Capella, 420). Third, the

relative amounts of heavy elements change drastically

between different document areas and from manuscript to

manuscript, with no historical trend. Fourth, there is, as

expected, a direct correlation between the quality of

attenuation-contrast images and the chemical composition.

In the best situations the X-ray attenuation image quality

is good enough to perform tomographic reconstruction of

phantom ‘volumes’ created by stacking ancient manuscript

fragments. In the worst cases, even simple visualization is a

problem.

In such cases, the properties of synchrotron light become

very helpful. Indeed we exploited its spatial coherence

(Margaritondo, 2002) to record images with refractive-index

contrast. As demonstrated by the extensive experience (Hwu

et al., 1999) with other types of specimens, this could allow the

recognition of faded-out or very weak characters.

2. Chemistry of ancient inks in everyday administrativewritings

Why could heavy elements be present in ancient inks? Let

us start from black inks (Yale University Library Special

Collections Conservator Unit, 2012; Capella, 420). For many

centuries, Europe widely used a formula generically denomi-

nated as ‘iron gall’, a name suggesting the presence of iron. A

less common black ink, with no heavy elements, was the

Roman atramentum scriptorium, based on lampblack with a

gum binder.

In addition to black inks, part of the documents, typically

those with important writings, used coloured inks. Some of

them contained heavy elements, e.g. mercury in cinnabar red

(Delaney et al., 2014). Other common recipes did not use

heavy elements, e.g. the Brazil red (Yale University Library

Special Collections Conservator Unit, 2012).

Even the generic iron gall formula corresponded to a wide

variety of ingredients and recipes (Yale University Library

Special Collections Conservator Unit, 2012). The basic fabri-

cation process was the reaction of an acid with an iron

compound. The most common procedure involved tannic acid

(C76H52O46) and iron sulfate (FeSO4) in rainwater, white wine

or vinegar (Smith, 2009).

Tannic acid was obtained from plants, the richest source

being the ‘galls’ produced by trees in response to parasite

attacks (e.g. by gall wasps); for example, the British oak galls

or the top-quality ‘Aleppo galls’. Iron sulfate was known as

‘green vitriol’, extracted from mines, notably coal mines. The

reaction of tannic acid with FeSO4 produced, with oxygen

exposure, ferrotannate, a black pigment.

In addition to the pigment, the black inks also contained a

water-soluble binder. One of the most common was gum

arabic. This is a natural product of trees, e.g. acacia, rich in

polysaccharides and glycoproteins; its main component is

arabin (Smith, 2009; Ruggiero, 2002), the calcium salt of the

polysaccharide arabic acid. Other ingredients could be

present, such as logwood pigment.

One important property of iron gall inks is their time

evolution. Although a small quantity of black pigment is

developed with the oxygen present in the solution, most is

produced with atmospheric oxygen after writing, over hours or

days.

Furthermore, the ink is corrosive over very long periods of

time, chemically attacking the substrate. The ink–substrate

interaction was extensively analyzed by Banik et al. (1983);

and Neevel & Reissland (1997), Proost et al. (2004) and

Kanngiesser et al. (2004) attacked this issue with synchrotron

radiation XANES (X-ray absorption near-edge structure) and

microfluorescence techniques.

The above features agree with our chemical analysis, based

on XRF. We performed the XRF experiments with a portable

m-XRF spectrometer ARTAX (model 200; Brucker). This

instrument uses an air-cooled fine-focus Mo X-ray source with

a collimator. The detector is a Peltier cooled silicon drift

device with 10 mm2 active area, reaching a resolution better

than 150 eV for the Mn K� fluorescence, with a count rate up

to 105 s�1 and a dead time <10% at 4 � 104 s�1. The instru-

ment is equipped with a visible-light CCD camera (20�

magnification) and with a pointing laser, to identify and

picture the analyzed area. In our tests, XRF spectra were

recorded under He flux, operating the spectrometer at 15 kV

and 1500 mA (exposure time 180 s).

The specimens were carefully handled to avoid contam-

ination but posed no particular fragility problems. The

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J. Synchrotron Rad. (2015). 22, 446–451 F. Albertin et al. � Ancient administrative handwritten documents 447

portable instrument enabled us to analyze whole manuscripts

and several micro-areas of each manuscript. Its performances

were perfectly adequate to our chemical analysis without

requiring a synchrotron source. In principle, the XRF instru-

ment could also yield images, but the corresponding time per

image would have been exceedingly long (several days per

picture) for our final objectives, and would exceedingly

complicate tomography.

Figs. 1–4 include XRF spectra taken from 200 mm-wide (the

collimator size) spots of 16th and 17th century Italian writings

of personal and administrative nature and from a 15th century

religious parchment manuscript. We acquired them using the

same geometric conditions for all specimens.

All spectra revealed Fe in the ink areas, as opposed to the

substrate areas. In addition, we detected Ca in the same ink

areas. This is consistent with the use of gum arabic as the

binder. Calcium was also found in the substrate of the

parchment specimens presumably due to chalk used during

support preparation (Van der Snickt et al., 2008).

These rather straightforward results are accompanied by

several other findings. In the 1590 (Fig. 1) and 1664 (Fig. 3)

specimens the ink also contains Cu and Zn, which are known

to contribute to the ink–substrate interaction (Banik et al.,

1981). Furthermore, the Fe and Ca content varied substan-

tially. We reached this semi-quantitative conclusion using

spectra recorded with geometric, voltage and current condi- tions as similar as possible for different specimens and

areas.

The different amounts of Fe correlate well with the X-ray

attenuation contrast, as shown in Figs. 1–4. These figures

include visible photographs as well as X-ray attenuation

images.

The radiographs were taken at the TOMCAT beamline

(Stampanoni et al., 2007) of the Swiss Light Source, Paul

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448 F. Albertin et al. � Ancient administrative handwritten documents J. Synchrotron Rad. (2015). 22, 446–451

Figure 1Results for a 1590 Italian (Tuscany) handwritten record. Top right: X-rayfluorescence spectra taken from the 200 mm-wide spots marked on thetop-left visible picture. Bottom: comparison of a 14 mm � 18 mm visiblepicture (left) with an X-ray image taken in the free propagation mode ofthe TOMCAT beamline (15 keV, exposure time 80 ms) (Stampanoniet al., 2007). In this acquisition mode, two X-ray effects are visible:attenuation allows character recognition whereas phase contrastenhances the paper fibres.

Figure 2Results like those of Fig. 1, for a 1646 Italian (Tuscany) specimen (imagesize 18 mm � 14 mm). Here, the iron concentration in the ink is too lowto detect characters with X-ray attenuation whereas the paper fibres arestill visible by phase contrast.

Figure 3Results like those of Fig. 1, for a 1664 Italian (Tuscany) specimen (imagesize 18 mm � 14 mm). The radiograph reveals otherwise nearly invisibleholes caused by ink-induced paper corrosion.

Scherrer Institute. The X-ray source was a 2.9 T superbending

magnet with a critical photon energy of 11.1 keV, and an

electron beam (source) size of 46 mm � 16 mm. The main

optical component is a fixed-exit double-crystal multilayer

monochromator that covers the energy range 6–45 keV. The

crystal optics is mounted on two independent high-precision

goniometers. The first crystal has motorized pitch, roll and

horizontal translation; the second crystal has the same degrees

of freedom and, in addition, yaw and vertical translation. The

entire system is positioned on a base plate that can be verti-

cally adjusted. The vertical size of the beam is ‘controlled’ by

moving the end-station along the beam path (up to 15 m travel

range).

For the images of Figs. 1–3, the photon energy was 15 keV,

and 25 keV for Fig. 4. Throughout the image-recording

experiments the storage ring current was kept constant at

400 mA by operation in the top-up mode.

TOMCAT can record images with different modes,

described in detail by Stampanoni et al. (2007). The images in

Figs. 1–3 were taken with the free-propagation operation

mode and reflect both phase contrast and attenuation contrast.

Phase contrast is primarily visible in the microscopic substrate

features. Attenuation contrast prevails in the ink areas.

The effects of iron on X-ray attenuation contrast are visible

when comparing Fig. 1 and Fig. 3 with Fig. 2: in the 1646

specimen the Fe peak is rather weak and the X-ray image

shows no clear evidence of characters.

In addition to black (iron gall) ink, ancient manuscripts

could also have colour inks. Our 15th century parchment

specimen included red characters, written with ink containing

Hg (cinnabar). Hg was indeed detected in the X-ray fluores-

cence spectra, as seen in Fig. 4, and produced excellent

attenuation contrast. On the contrary, the Fe signal from the

black characters is weak, and the contrast low.

Positive tests of tomographic reconstruction are shown in

Fig. 5 for a 1679 specimen, consisting of a stack of eight 0.8 cm-

diameter fragments simulating a small volume. We took a set

of projection images over a � rad range, at an angular distance

of �/103 from each other, using 15 keV photons and a time

exposure of 10 ms per picture.

Fig. 5 shows three tomographically reconstructed ‘pages’

with recognizable characters (comparable results were

obtained for the other pages) and two three-dimensional

reconstructed side views. Note that the spatial resolution

(6.5 mm detector pixel) is largely sufficient not only to distin-

guish different ‘pages’ but also to determine whether the

writing is on the front or on the back of each ‘page’.

3. Alternate imaging modes

How could we handle the cases of low attenuation contrast?

Synchrotron light can provide the answer, allowing imaging

techniques with contrast mechanisms related to the imaginary

part of the complex refractive index, i.e. to phase-related

phenomena like refraction (Margaritondo & Hwu, 2013).

Fig. 6 shows a test: the imaged area is the same as that of

the red characters of Fig. 4, but the contrast mechanism

is different. The image pair was recorded using differential

phase contrast (DPC), discussed in detail by Weitkamp et al.

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J. Synchrotron Rad. (2015). 22, 446–451 F. Albertin et al. � Ancient administrative handwritten documents 449

Figure 5Tomography results for a 1679 Italian (Tuscany) document. Centre: threereconstructed images of virtual ‘pages’ with different characters,corresponding to the visible photographs on the left-hand side. Right:three-dimensional reconstructions showing side views of the pages withink visible over them. The tomography was performed for a stack of eightmanuscript fragments simulating a small volume. The bright area in thetwo right-hand-side images is a small magnet keeping the fragment stackin place.

Figure 4Results similar to those of Fig. 1, for 15th century religious writing onparchment, of Italian origin (image size 18 mm� 7 mm). The bottom partshows a comparison of two visible pictures of red and black ink charactersand two X-ray absorption images below (recorded with a gratinginterferometer at TOMCAT, DPC mode, 25 keV, exposure time 80 ms)(Stampanoni et al., 2007).

(2005). With suitable digit-by-digit mathematical processing

(Weitkamp et al., 2005), the raw DPC images yield pictures

corresponding to absorption, scattering and refraction. Fig. 4

shows indeed DPC absorption-contrast images obtained in

this way. Fig. 6 shows instead scattering and refraction images.

The important point here is that the refraction images

reflect the local specimen morphology rather than only its

chemical composition. We can speculate that what we see in

Fig. 6 reflects the substrate morphology modified by the

writing process or by the ink–substrate interaction. This could

be used to detect a character when the attenuation contrast

gives a faint picture.

4. Conclusions and perspectives

Our tests yielded overall positive results along the path to

virtual X-ray reading but stressed some potential problems.

The positive point is that the European recipes to fabricate

common inks over several centuries produced in most cases

heavy elements sufficient for character detection by X-ray

attenuation. We verified that the corresponding image quality

is suitable for advanced tomographic reconstruction, at least

for a limited number of pages.

In some instances, however, the heavy-element content was

too weak. Our preliminary tests indicate that these cases can

be potentially handled with refraction images.

Note that the attenuation images and the refraction images

carry a wealth of information besides the written characters.

They can notably reveal information, complementary to other

experimental techniques (Proost et al., 2004; Kanngiesser et

al., 2004), related to the ink–substrate interaction, which in

many cases leads to corrosion and deterioration. This will

hopefully contribute to the identification of ways to prevent

long-term damage.

Results such as those discussed here open the way to a new

strategy for information harvesting from ancient documents,

alternate to page-by-page recording of visible pictures. A

single tomographic set could yield the same information more

rapidly and with minimized interaction with the document.

Many problems remain to be solved along this path: in

particular, we must test the extension of the tomographic

reconstruction to larger-size documents. Also crucial will be

the development of adequate software, for example for

automatic analysis of reconstructed images. However, the

technique must still be optimized to reach its best perfor-

mances. On a positive side, throughout our tests we found no

evidence whatsoever of radiation damage, consistent with

Patten et al. (2013).

The authors are grateful to Patrick Aebischer for his

leadership of the VTM project, to the Verbantiqua bookstore

(http://www.copernicum.it) for their generous donation of

antique manuscript specimens, to the staff of the Swiss Light

Source, Paul Scherrer Institut, for their outstanding technical

support, and to Professor Petrucci of the University of Ferrara

for his assistance in the chemical analysis and for several

stimulating discussions. The research was supported by the

Fonds National Suisse pour la Recherche Scientifique, the

Venice Time Machine Project, the Center for Biomedical

Imaging (CIBM),

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